With recent further integration of semiconductor integrated circuits, such as LSIs, circuit sizes and circuit line widths required of semiconductor devices have been miniaturized year by year. In order to form a circuit pattern of desired dimensions and line widths, a high-accuracy original pattern (reticle or mask) is required. As an example of a device for creating such an original pattern, there has heretofore been known a drawing device which employs a so-called lithography technique for drawing an original pattern, for example, by irradiating an electron beam onto a sample, such as a metal substrate (e.g., mask substrate), having a resist film applied thereto.
When an electron beam is irradiated onto a sample, such as a mask substrate, there would appear an influence called “proximity effect” that varies a size of a resist pattern formed on the sample. More specifically, the proximity effect is a phenomenon where the electron beam is irradiated even onto unintended portions of the sample due to front-scattered electron and backscattered electron produced by the irradiated electron colliding against the resist and metal substrate with the result that line widths etc. of the resist pattern are caused to vary depending mainly on a density of a circuit pattern. The conventionally-known drawing device would present the inconvenience that an adverse influence of the proximity effect becomes more noticeable with even further miniaturization of the circuit.
To address the foregoing inconvenience, there has been proposed an irradiation amount correction method which determines, in accordance with a density of a circuit pattern, an optimal electron beam irradiation amount of an electron beam (also referred to as “optimal irradiation amount” or “optimal dose amount”) to reduce the line width of a resist pattern etc. caused by a proximity effect. More specifically, according to the irradiation amount correction method, control is performed to reduce a time length of the electron beam irradiation in a region where the circuit pattern is dense because the substantive electron beam irradiation amount would become excessive in such a dense-circuit-pattern region, while control is performed to increase the time length of the electron beam irradiation in a region where the circuit pattern is coarse because the substantive electron beam irradiation amount would become insufficient or short in such a coarse-circuit-pattern region. Such arrangements can reduce line width variation of the resist pattern caused by the proximity effect. Among examples of the method for determining an optimal electron beam irradiation amount are ones disclosed in Non-patent Literature 1 and Patent Literature 1 identified below.